Spatial patterning of bird diversity by termite mounds across a human-modified African savanna landscape

Abstract

Ecologists have long been fascinated by the relationship between vegetation heterogeneity and biodiversity. Major contributors to heterogeneity include organisms that create regular vegetation patterns, such as mound-building termites, which concentrate nutrients, plant biomass, and some vertebrate distributions within ecosystems. Yet, little is known about how pattern-generating organisms affect biodiversity distributions across landscapes and in human modified ecosystems. Using a multi-scale approach, I examined the consequences of vegetated termite mounds for the distribution of birds across three ecosystems in a partially converted African savanna landscape. In Acacia-dominated savanna, saline grassland, and agricultural ecosystems of Gorongosa National Park and its buffer zone, I conducted point count surveys to estimate bird density (at the species, guild, or community level) and species richness in mound and matrix vegetation. Some bird species occurred at higher densities on mounds, while others, including some tree-dwelling species, occurred at higher densities in the matrix. In each ecosystem, avian abundance and species richness, including of functionally important guilds, were concentrated on mounds. Comparing between ecosystems, the composition of birds showed greater similarity on mounds than in the matrix. And, many savanna matrix-associated species were not detected under agricultural conversion, in areas lacking the natural heterogeneity of intact mound and matrix vegetation. Therefore, this research suggests limitations of termite mounds’ potential to maintain savanna biodiversity amidst anthropogenic pressure. The study informs a basic understanding of termite mounds as a key factor driving the distribution of African savanna bird diversity, including under agricultural conversion, at and below the landscape scale.